JP2007262507A - Palladium-plating liquid for electrolysis, and lead frame plated by using the liquid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a palladium-plating liquid for electrolysis, which imparts a plated film superior solder wettability, bonding strength to a wire or the like even though the plated film is thin, and to provide a lead frame showing the superior performances. <P>SOLUTION: The palladium-plating liquid for electrolysis includes: a water-soluble palladium salt; and naphthalene monosulfonic acid or naphthalene disulfonic acid, which may have a substituent, or a salt of them. The lead frame is sequentially formed of an electrolytically plated palladium film formed by using the liquid, an electrolytically plated nickel film, the above electrolytically plated palladium film, and an electrolytically plated gold film. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a palladium plating solution for electrolysis, and more specifically to a palladium plating solution for electrolysis containing a specific compound, and an electrolytic palladium plating film and a lead frame formed using the same.

  Noble metal plating using palladium is often applied to the junction terminal portion of an electronic device, and has attracted attention as a surface technology suitable for lead-free electronic components. Conventionally, lead frames have been plated with silver at the central wire bonding part and solder plating at the peripheral solder joints, but lead-free solder plating is technically incomplete. A -PPF (Pre-Platted-Frame) method has been put into practical use.

  FIG. 1 shows a general lead frame shape. In the Pd-PPF method, electrolytic nickel plating, electrolytic palladium plating, and electrolytic gold plating are sequentially performed on the entire surface of the lead frame to form a three-layer plating structure on the lead frame base material (copper, copper alloy, 42 materials, etc.). It is a method to make it.

  A chip is mounted on the center pad portion A of the lead frame, wire bonding is performed with the chip at the inner lead portion B, and the outer lead portion C is left and sealed with resin. The remaining outer lead portion C is used for soldering with the substrate.

  Although the Pd-PPF method has reached a satisfactory level in terms of performance, the biggest problem is cost. Palladium and gold are more expensive than current silver and solder, and it is necessary to reduce the thickness of the electrolytic palladium plating film and the electrolytic gold plating film to the minimum level in order to reduce the manufacturing cost of the lead frame.

  However, solder wettability deteriorates when a thin film is used. As for the palladium plating solution for electrolysis, there are Patent Documents 1 to 4, but these techniques do not have sufficient solder wettability.

Japanese Patent Laid-Open No. 07-011475 JP 07-278870 A JP 11-043796 A JP 2001-262390 A

  The present invention has been made in view of the above-mentioned background art, and its problem is to provide a palladium plating solution for electrolysis that provides a plating film excellent in solder wettability, wire bonding strength, etc. even if it is thinned. Moreover, it is providing the lead frame excellent in the said performance.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor has shown good solder wettability and wire bonding strength even in a thin film by including a specific substance in the palladium plating solution for electrolysis. It has been found that the above problems can be achieved, and the present invention has been achieved.

  That is, the present invention provides a palladium plating solution for electrolysis characterized by containing a water-soluble palladium salt and an optionally substituted naphthalene monosulfonic acid or naphthalene disulfonic acid or a salt thereof. It is.

  The present invention also provides an electrolytic palladium plating film formed using the above palladium plating solution for electrolysis.

  The present invention also provides a lead frame in which an electrolytic nickel plating film, an electrolytic palladium plating film, and an electrolytic gold plating film are sequentially formed on a metal substrate, the electrolytic palladium plating film comprising the above palladium plating solution for electrolysis. The present invention provides a lead frame characterized by being formed by using.

  According to the present invention, even when the electrolytic palladium plating film and / or the electrolytic gold plating film formed thereon is a thin film, it is possible to achieve good solder wettability and excellent wire bonding strength. A liquid can be provided.

  Hereinafter, the present invention will be described, but the present invention is not limited to the following specific embodiments, and can be arbitrarily modified and implemented.

The palladium plating solution for electrolysis of the present invention is an essential component,
(1) It contains a water-soluble palladium salt, and (2) an optionally substituted naphthalene monosulfonic acid or naphthalene disulfonic acid or a salt thereof (hereinafter abbreviated as “naphthalenesulfonic acid compound”). It is characterized by.

  The water-soluble palladium salt is not particularly limited, but palladium chloride, palladium sulfate, palladium nitrate, palladium phosphate, palladium sulfite and the like are preferable. Moreover, these ammonia complexes (ammine complexes) or these amine complexes are also preferable. Particularly preferred is dichlorotetraamminepalladium.

  The concentration of the water-soluble palladium salt in the palladium plating solution for electrolysis of the present invention is not particularly limited, but is 0.1 g / L to 50 g / L in terms of palladium with respect to the entire palladium plating solution for electrolysis. 1 g / L to 40 g / L is particularly preferable, and 2.5 g / L to 30 g / L is more preferable.

  If it is less than 0.1 g / L, burns may occur and a normal film may not be obtained, which may be impractical. On the other hand, when the amount is more than 50 g / L, palladium metal is consumed due to the liquid drawing, which is not economical. These salts may be used alone or in combination of two or more.

The palladium plating solution for electrolysis of the present invention must contain a “naphthalenesulfonic acid compound”. The “naphthalene sulfonic acid compound” refers to naphthalene monosulfonic acid, naphthalene disulfonic acid or a salt thereof which may have a substituent as described above. That is, the “naphthalene sulfonic acid compound”
(A) Naphthalene monosulfonic acid or a salt thereof which may have a substituent, or (b) Naphthalene disulfonic acid or a salt thereof which may have a substituent. The sulfonic acid group is directly bonded to the naphthalene ring.

  Here, the substituent is directly bonded to the naphthalene ring, and specific examples include an alkyl group, an alkoxyl group, a hydroxyl group, an amino group, an alkylamino group, a carboxyl group, and a carboxyester group. The substituent is arbitrarily selected in consideration of the fact that the naphthalenesulfonic acid compound having the substituent is water-soluble, and the inclusion thereof does not adversely affect the performance of the palladium plating solution for electrolysis. The alkyl group as a substituent is preferably an alkyl group having 1 to 5 carbon atoms.

The naphthalene ring of the naphthalenesulfonic acid compound may or may not be bonded to a substituent other than the sulfonic acid group, but is preferably not bonded. That is, what is represented by General formula (1) is preferable.
[In General Formula (1), X represents a counter cation of sulfonic acid. ]

In general formula (1), X represents a cation of a sulfonic acid. The cation (X) of the sulfonic acid in the palladium plating solution for electrolysis of the present invention depends on other components such as a conductive salt and a pH adjuster in the palladium plating solution for electrolysis, and is particularly limited. And any monovalent cation. Usually, alkali metal ions such as sodium ion (Na ⁺ ) and potassium ion (K ⁺ ); quaternary ammonium ions such as ammonium ion (NH ₄ ⁺ ) and alkylammonium ion; hydrogen ion (H ⁺ ) and the like.

  In the case of a disulfonic acid compound, the two sulfonic acid groups need only be directly bonded to the naphthalene ring, and even if both are bonded to one ring (position 1, 2, 3 or 4), May be bonded to each other ring (position 1, 2, 3 or 4 and position 5, 6, 7 or 8), but they are bonded to different rings from the viewpoint of sufficiently high water solubility. It is preferable.

  The naphthalene sulfonic acid compound used for the preparation of the palladium plating solution for electrolysis of the present invention may be any water-soluble compound that has the above structure when dissolved in water to form a palladium plating solution for electrolysis. Specifically, for example, 1-naphthalenesulfonic acid, 1-naphthalenesulfonic acid sodium, 1-naphthalenesulfonic acid potassium, 1-naphthalenesulfonic acid ammonium, 2-naphthalenesulfonic acid, 2-naphthalenesulfonic acid sodium, 2-naphthalene Potassium sulfonate, ammonium 2-naphthalenesulfonate, 2,7-naphthalenedisulfonic acid, potassium 2,7-naphthalenedisulfonate, sodium 2,7-naphthalenedisulfonate, ammonium 2,7-naphthalenedisulfonate, 1,5- Preferred examples include naphthalenedisulfonic acid, potassium 1,5-naphthalenedisulfonate, sodium 1,5-naphthalenedisulfonate, ammonium 1,5-naphthalenedisulfonate, and the like. These may use 1 type, but can also use 2 or more types together.

  Those having 3 or more sulfonic acid groups bonded to the naphthalene ring cannot be used for solving the problems of the present invention because solder wettability is not improved and wire bonding properties are somewhat inferior.

  The content of the naphthalenesulfonic acid compound is not particularly limited, but it is preferably contained in the range of 0.001 g / L to 50 g / L with respect to the entire palladium plating solution for electrolysis, 20 g / L is more preferable, and 1.0 g / L to 10 g / L is most preferable. If the content of the naphthalene sulfonic acid compound is too small, improvement in solder wettability may not be obtained.

  The palladium plating solution for electrolysis of the present invention can further contain a conductive salt, a chelating agent, a surfactant and the like as necessary.

  The conductive salt is not particularly limited, but is appropriately selected from ammonium nitrate, potassium nitrate, sodium nitrate, ammonium sulfate, potassium sulfate, sodium sulfate, ammonium phosphate, potassium phosphate, sodium phosphate, ammonium chloride, potassium chloride, sodium chloride, and the like. You can select and use. These may use 1 type, but can also use 2 or more types together.

  Examples of the chelating agent include ethylenediaminetetraacetic acid, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, dicarboxymethylglutamic acid, 1,3-propanediaminetetraacetic acid, and other aminocarboxylic acid chelating agents or salts thereof; , 3-diamino-2-hydroxypropanetetraacetic acid, dihydroxyethylglycine, hydroxyethyliminodiacetic acid, hydroxyaminoacetic acid-based chelating agents such as hydroxyethylethylenediaminetriacetic acid, triethanolamine or salts thereof; hydroxyethylidene diphosphonic acid; Phosphonic acid chelating agents such as nitrilotri (methylenepropanephosphonic acid), phosphonobutane triacetic acid, ethylenediaminetetra (methylenephosphonic acid) or their salts; oxalic acid, citric acid, tartaric acid, gluco Use carboxylic acids such as acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, lepargic acid, sebacic acid, maleic acid, fumaric acid, acetic acid, propionic acid and their salts be able to. These may use 1 type, but can also use 2 or more types together.

  As the surfactant, it can be used by appropriately selecting from existing cationic, nonionic, cationic, zwitterionic and the like. These may use 1 type, but can also use 2 or more types together.

  Examples of the cationic surfactant include alkyl sulfate ester salt, polyoxyethylene alkyl ether sulfate ester salt, alkylbenzene sulfonate salt, fatty acid salt, naphthalene sulfonate formalin condensate, and polymer surfactant.

  Nonionic surfactants include polyoxyalkylene alkyl ethers such as polyoxyethylene alkyl ethers; polyoxyethylene derivatives, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxy Examples include ethylene fatty acid esters, polyoxyethylene hydrogenated castor oil, polyoxyethylene alkylamines, and fatty acid alkanolamides.

  Examples of cationic surfactants include alkylamine salts and quaternary ammonium salts, and examples of amphoteric surfactants include alkylbetaines and alkylamine oxides.

  The pH of the palladium plating solution for electrolysis according to the present invention is preferably in the range of 4 to 12, particularly preferably in the range of 7 to 9. If the pH is too low, palladium may be precipitated, and if it is too high, the resist attached to the substrate may be dissolved.

  The bath temperature during plating of the palladium plating solution for electrolysis of the present invention is not particularly limited, but it is preferably used in the range of 30 to 80 ° C.

Further, there is no particular limitation current density when performing plating using electrolytic palladium plating solution of the present invention, preferably used in an amount of ^{0.25A / dm 2 ~50A / dm 2} , 0.3A / Dm ^{2 to} 10 A / dm ² is particularly preferable.

  The electrolytic palladium plating time is not particularly limited, and the thickness of the electrolytic palladium plating film using the palladium plating solution for electrolysis of the present invention is usually 0.001 μm to 0.1 μm, preferably 0.002 μm to 0.05 μm. Particularly preferably, the thickness is 0.005 μm to 0.02 μm. If the electrolytic palladium plating film is too thin, good solder wettability and excellent wire bonding strength may not be achieved. On the other hand, when the electrolytic palladium plating film is too thick, it is disadvantageous in terms of cost. Also, even if the present invention is a thin film, the solder wettability and wire bonding performance are good, so the above effects of the present invention cannot be utilized. There is a case.

  When performing Pd-PPF (Pre-Plated-Frame) (hereinafter abbreviated as “PPF”) treatment on a lead frame using the palladium plating solution for electrolysis of the present invention, the base material copper, copper alloy or 42 materials Etc., by performing a known electrolytic nickel plating process, an electrolytic palladium plating process using the palladium plating solution for electrolysis of the present invention, and a known electrolytic gold plating process.

  As an electrolytic nickel plating bath, a Watt bath, a sulfamine bath, or the like can be used. As an electrolytic gold plating solution, a commercially available pure gold plating solution, for example, an after plate (trade name) manufactured by Japan High Purity Chemical Co., Ltd., etc. It can be used.

<Action and principle>
When an electrolytic palladium plating film is formed using the palladium plating solution for electrolysis containing the naphthalenesulfonic acid compound of the present invention, good solder wettability even if the electrolytic palladium plating film and / or the electrolytic gold plating film is a thin film. Although the action and principle that can achieve excellent wire bonding strength are not clear, the technical scope of the present invention is not limited by the action principle, but it is presumed as follows. That is, the electrolytic palladium plating film formed by using the palladium plating solution for electrolysis of the present invention is excellent in the property of preventing the diffusion of copper and nickel even if it is a thin film. It is presumed that it was able to prevent adverse effects on solder wettability and wire bonding properties.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not limited to these Examples, unless the summary is exceeded.

<Measuring method of each plating step and thickness of plating film>
The lead frame on which the plating film is to be formed is immersed in a cyan-based degreasing solution (sodium cyanide 50 g / L, sodium hydroxide 100 g / L, EDTA · disodium salt 50 g / L) at room temperature and cathode voltage 5.0 V for 10 seconds. Degreasing treatment was performed. Then, it was immersed in 5 mass% sulfuric acid of normal temperature for 30 seconds.

Next, a sulfamic acid matte nickel solution made under the standard use conditions of a commercially available SN conch (trade name manufactured by Murata Co., Ltd.) was used, and the temperature was 50 ° C. and the cathode current density was 5.0 A / dm ² . A degree of electrolytic nickel film was formed.

  Here, the film thickness of the electrolytic nickel plating film was measured with a micro fluorescent X-ray analyzer SEA5120 (trade name, manufactured by Seiko Instruments Inc.). The film thickness of the electrolytic palladium plating film after this and the film thickness of the electrolytic gold plating film were also measured with the same apparatus.

Subsequently, using the palladium plating solution for electrolysis of the present invention, electrolytic palladium plating treatment was performed at a temperature of 60 ° C. and a cathode current density of 0.5 A / dm ² so as to achieve the target film thickness of each of the following Examples and Comparative Examples. Went.

Subsequently, an electrolytic gold plating film having a temperature of 50 ° C. and a cathode current density of 0.09 A / dm ² was formed on a commercially available electrolytic gold plating solution afterplate (trade name, manufactured by Nippon Kojun Kagaku Co., Ltd.). .

<Measurement method of wire bonding strength>
FIG. 2 shows a schematic diagram of a method for measuring wire bonding strength. After the lead frame formed by the method described in the description of the plating step is heated in an oven at 240 ° C. for 30 seconds, a wedge-wedge bonder WEST BOND 5400-45G (manufactured by WEST BOND) is used for the pad portion. Gold wire diameter 25 μmφ, load 80 g, temperature 120 ° C., ultrasonic power 1 is 1000 mW, 35 msec, ultrasonic power 2 is 1000 mW, 35 msec, and wire is pulled in the “pull test pull direction” shown in FIG. The peel strength immediately before the breakage of the gold wire and the breakage point of the gold wire were observed. The case where the peel strength was 8.0 g or more and the fractured portion in FIG. 2 was a “n” in the neck was defined as “good”, and the case where the wire peeled off was “x” was defined as “bad”.

<Measuring method of solder wettability by meniscograph method>
FIG. 3 shows the measurement principle of the meniscograph. It should be noted that although the molten solder actually rises, the sample descends for simplicity. The lead frame on which the plating film was formed was heated in an oven at 400 ° C. for 60 seconds, and then the outer lead part was cut off, and a flux (SOLDERITE NA-200, manufactured by Tamura Chemical Co., Ltd.) was applied to the tip. The above measurement sample is held in a menisograph solder wettability measuring instrument (RHESCA, SAT5100) in which lead-free solder (Senju Metal Co., Sn96.5% Ag3% Cu0.5%) is melted at 250 ° C. The attached chuck was attached.

  The solder pot of the measuring device rises at a speed of 10 mm / sec (A to B in FIG. 3). When the sample is immersed in the solder by 5.0 mm, the rise of the solder pot stops (C in FIG. 3), and lowers 5.0 seconds after the sample comes into contact with the solder (B in FIG. 3) (F in FIG. 3). ). The force applied to the sample is determined by the size of the buoyancy of the immersed part of the sample and the force with which the solder wets the sample surface. By coming into contact with the solder, the force that was initially upward due to the buoyancy from the solder becomes a downward force due to wetting. When the two forces are the same as before the contact with the solder (B in FIG. 3) after contact with the solder (D in FIG. 3), this is called “zero cross time”. Among them, those having a time from B to D) of 2 seconds or less were evaluated as “good”. Similarly, three measurements were performed from n = 1 to n = 3.

<Method for evaluating plating running performance>
Electrolytic plating was performed on 1 L of the palladium plating solution for electrolysis using a 0.1 dm ² degreased copper plate. While replenishing the amount of palladium consumed as needed, measure the total amount of palladium consumed / the amount of palladium in the bath (hereinafter referred to as “MTO”), and “solder wettability” with the solution after consuming up to 3 MTO of palladium. Was measured. When the “solder wettability” at this time did not change from the time of the new construction bath, it was determined that the plating running property was excellent.

Example 1
A palladium plating solution for electrolysis having the following composition was prepared, and the pH was adjusted to 7.5 to 8.5 with aqueous ammonia and phosphoric acid.
Dichlorotetraamminepalladium 3.0 g / L (in terms of palladium)
2-Naphthalenesulfonic acid sodium salt 3.0g / L
Ammonium nitrate 125g / L
Ammonium acetate 50g / L
Ammonium chloride 10g / L

  After forming a 1.0 μm electrolytic nickel plating film on the pad portion of the copper lead frame shown in FIG. 1 by the above method, 0.01 μm electrolytic palladium plating by the above method using the above palladium plating solution for electrolysis. Then, a 0.005 μm electrolytic gold plating film was formed by the above method.

  When the wire bonding strength was measured on the plating frame thus obtained, the average peel strength of 20 pieces was 9.1 g, and the evaluation of the breaking points was all “◯”. It was.

Example 2
A palladium plating solution for electrolysis having the same composition as in Example 1 was prepared, and the pH was adjusted to 7.5 to 8.5 with ammonia and phosphoric acid. A plating frame was obtained in the same manner as in Example 1 except that the thickness of the electrolytic palladium plating film was changed to 0.03 μm.

  The plating frame thus obtained was heated in an oven at 400 ° C. for 60 seconds, and the solder wettability of the outer lead portion was evaluated. As shown in Table 1, the results were good both at the time of new building bath and after 3 MTO, and were excellent in plating running performance.

Example 3
Prepare a palladium plating solution for electrolysis having the following composition, adjust the pH to 7.5 to 8.5 with ammonia and phosphoric acid, obtain a plating frame as in Example 2, and solder as in Example 2. The wettability was measured. As shown in Table 1, the results were good both at the time of new building bath and after 3 MTO, and were excellent in plating running performance.

Bis (ethylenediamine) palladium chloride 3.0g / L (in terms of palladium)
1,5-Naphthalenedisulfonic acid disodium 3.0 g / L
Sodium sulfate 125g / L
Sodium succinate 50g / L
Ammonium chloride 10g / L

Comparative Example 1
A plating frame was obtained in the same manner as in Example 2 except that sodium 2-naphthalenesulfonate in the palladium plating solution for electrolysis in Example 2 was replaced with trisodium naphthalene-1,3,6-trisulfonate. Similarly to 2, solder wettability was measured. As shown in Table 1, the results were inferior both at the time of new construction and after 3 MTO. Moreover, when the wire bonding test was also performed in the same manner as in Example 1, the evaluation of the breaking points was “◯” for all 20, but the average peel strength of the 20 pieces was 7.1 g, which was inferior.

Comparative Example 2
A plating frame was obtained in the same manner as in Example 2 except that sodium 2-naphthalenesulfonate in the palladium plating solution for electrolysis in Example 2 was omitted, and the solder wettability was measured in the same manner as in Example 2. As shown in Table 1, the results were inferior both at the time of new construction and after 3 MTO.

Comparative Example 3
A plating frame was obtained in the same manner as in Example 2 except that sodium 2-naphthalenesulfonate in the palladium plating solution for electrolysis in Example 2 was replaced with β-naphthol ethoxylate (2-naphthol ethylene oxide 12-mole adduct). In the same manner as in Example 2, the solder wettability was measured. As shown in Table 1, the results were inferior after 3MTO, and the plating running performance was poor.

Comparative Example 4
A plating frame was obtained in the same manner as in Example 2 except that sodium 2-naphthalenesulfonate in the palladium plating solution for electrolysis in Example 2 was replaced with sodium 3-pyridinesulfonate, and solder wettability in the same manner as in Example 2. Was measured. As shown in Table 1, the results exceeded 2 seconds both at the time of new construction bath and after 3 MTO, and the solder wettability was inferior.

The numbers in Table 1 are the time from B to D in FIG. 3, and the unit is “second”.

  In the above examples and comparative examples, only the electrolytic palladium plating on the lead frame has been described. However, the fact that good results were obtained by the above measurement was also applied to connectors, board terminals, etc. It is clear that it exhibits a good effect.

  The plating film formed by using the palladium plating solution for electrolysis of the present invention is excellent in solder wettability, its running property, and wire bonding property, and is therefore widely used for lead frames, connectors, board terminals and the like. .

It is a figure which shows the general lead frame used by the Example and comparative example of this invention. It is a figure which shows the outline of the measuring method of "wire bonding strength" used in the Example of this invention. That is, it is a diagram showing a method of measuring “peel strength” and a criterion for “evaluation of broken part”. The peeling of the wire is the breaking point evaluation “×”, and the broken neck is the breaking point evaluation “◯”. It is a figure which shows the measuring method of the "solder wettability" by the meniscograph method used by the Example and comparative example of this invention.

Claims (7)

  A palladium plating solution for electrolysis comprising a water-soluble palladium salt and naphthalene monosulfonic acid or naphthalene disulfonic acid which may have a substituent or a salt thereof.   The optionally substituted naphthalene monosulfonic acid or naphthalene disulfonic acid or a salt thereof is naphthalene monosulfonic acid or naphthalene disulfonic acid, a sodium salt thereof, a potassium salt thereof or an ammonium salt thereof. 2. The palladium plating solution for electrolysis according to 1.   The water-soluble palladium salt is palladium chloride, palladium sulfate, palladium nitrate, palladium phosphate or palladium sulfite, or an ammonia complex or amine complex thereof. The palladium plating solution for electrolysis as described in 2.   The naphthalene monosulfonic acid or naphthalene disulfonic acid or a salt thereof which may have the substituent is contained in an amount of 0.001 g / L to 50 g / L with respect to the entire plating solution. Item 4. A palladium plating solution for electrolysis according to Item 3.   5. The water-soluble palladium salt according to claim 1, wherein the water-soluble palladium salt is contained in an amount of 0.1 g / L to 50 g / L in terms of palladium with respect to the entire plating solution. Palladium plating solution for electrolysis.   An electrolytic palladium plating film formed using the palladium plating solution for electrolysis according to any one of claims 1 to 5. 6. A lead frame in which an electrolytic nickel plating film, an electrolytic palladium plating film, and an electrolytic gold plating film are sequentially formed on a metal substrate, wherein the electrolytic palladium plating film is any one of claims 1 to 5. A lead frame formed using the palladium plating solution for electrolysis described in 1.